Apparatus and methods for cooling network switches

ABSTRACT

The disclosed embodiments include a plurality of plenums for distributing cooling air throughout the switch. The switch is divided into separate cooling domains. Each PCB receives a separate supply of cooling air, so that no PCB is located upstream or downstream from another PCB. The present embodiments thus eliminate the problem of stack rise, which can decrease switch performance.

BACKGROUND

1. Technical Field

The present disclosure relates to cooling in network switches.

2. Related Art

A computer network is an interconnected group of computers and otherdevices, such as storage devices. All networks are made up of basichardware building blocks to interconnect network nodes. These buildingblocks include network interface cards (NICS), bridges, hubs, switches,and routers, for example. Each device in the network is called a node.All nodes include at least one port. An interconnect medium, such ascopper wiring or optical cabling, extends between device ports.

FIG. 1 is a schematic block diagram of a typical network 30. The network30 includes a plurality of interconnected devices, including first andsecond switches 32, 34, a host system 33 coupled to the second switch34, a disk array 36 coupled to the first switch 32, and a server 38coupled to both switches 32, 34 and to storage 40.

A switch is a multi-port device in which each port manages a simplepoint-to-point connection between itself and its attached system. Eachswitch port can be attached to a host system, a server, a peripheral, anI/O subsystem, a bridge, a hub, a router, or even another switch. Aswitch receives data packets from one port and automatically routes themto other ports based on addresses contained in the packets.

Switches include a plurality of modules supported by a chassis. Themodules are printed circuit boards (PCBs), and include one or moreintegrated circuit (IC) devices, or chips, on at least one surface. Inoperation the chips generate heat that must be dissipated in order tokeep the switch operating efficiently. One problem that plagues switchcooling is “stack rise.” Stack rise occurs when cooling air passes overmultiple chips in succession. Each chip heats the passing cooling air sothat downstream chips always receive warmer, or preheated, cooling air.These downstream chips are more susceptible to overheating, whichdecreases switch performance.

SUMMARY

The preferred embodiments of the present apparatus and methods forcooling network switches have several features, no single one of whichis solely responsible for their desirable attributes. Without limitingthe scope of the present embodiments as expressed by the claims thatfollow, their more prominent features now will be discussed briefly.After considering this discussion, and particularly after reading thesection entitled “Detailed Description of the Preferred Embodiments,”one will understand how the features of the present embodiments provideadvantages, which include a decreased likelihood of a decline in switchperformance due to overheating.

One aspect of the present apparatus and methods for cooling networkswitches includes the realization that stack rise is detrimental tomaintaining switch performance. Accordingly, if stack rise could beeliminated from a switch the switch would be less likely to suffer adecline in performance.

One embodiment of the present network switch comprises a plurality ofspaced printed circuit boards (PCBs), a plurality of fan modulesconfigured to force cooling air through the switch, and a plurality ofplenums configured to carry the forced cooling air. Each plenum isassociated with at least one of the fan modules. The plenums areconfigured to distribute the cooling air throughout the switch so thatno PCB is located upstream from any other PCB, and therefore no PCBpreheats the cooling air received by any other PCB.

In one embodiment of the present methods for cooling a network switch,the switch includes a plurality of spaced printed circuit boards (PCBs).Each PCB includes at least one integrated circuit (IC) device thereon.The method comprises the steps of forcing cooling air through the switchsuch that each of the plurality of spaced PCBs receives cooling air, anddistributing the cooling air throughout the switch such that no PCB islocated upstream from any other PCB, and therefore no PCB preheats thecooling air received by any other PCB.

Another embodiment of the present network switch comprises a pluralityof spaced printed circuit boards (PCBs), a plurality of fan modulesconfigured to force cooling air through the switch, a plurality ofplenums configured to carry the forced cooling air. Each plenum isassociated with at least one of the fan modules. The plenums areconfigured to distribute the cooling air throughout the switch so thatcooling air entering the switch passes across only one of the PCBsbefore exiting the switch.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiments of the present apparatus and methods forcooling network switches now will be discussed in detail with anemphasis on highlighting the advantageous features. These embodimentsdepict the novel and non-obvious apparatus and methods shown in theaccompanying drawings, which are for illustrative purposes only. Thesedrawings include the following figures, in which like numerals indicatelike parts:

FIG. 1 is a schematic block diagram of a typical computer network;

FIG. 2 is a schematic, side elevation view of one embodiment of thepresent network switch illustrating a method and apparatus for coolingthe switch;

FIG. 3 is a schematic, cross-sectional, top plan view of the switch ofFIG. 1, taken through the line 3-3 in FIG. 1;

FIG. 4 is a schematic, cross-sectional, top plan view of the switch ofFIG. 1, taken through the line 4-4 in FIG. 1;

FIG. 5 is a schematic, rear elevation view of the push domain of theswitch of FIG. 1;

FIG. 6 is a schematic, cross-sectional, top plan view of an alternateconfiguration for the present switch;

FIG. 7 is a schematic, rear elevation view of the switch of FIG. 6;

FIG. 8 is a schematic, side elevation view of another embodiment of thepresent network switch illustrating a method and apparatus for coolingthe switch;

FIG. 9 is a schematic, side elevation view of another embodiment of thepresent network switch illustrating a method and apparatus for coolingthe switch;

FIG. 10 is a schematic, side elevation view of another embodiment of thepresent network switch illustrating a method and apparatus for coolingthe switch;

FIG. 11 is a schematic, side elevation view of one embodiment of a pulldomain of the present switch;

FIG. 11A is a detail view of a portion of the pull domain of FIG. 11;

FIG. 12 is a schematic, side elevation view of one embodiment of a pushdomain of the present switch;

FIG. 13 is a schematic, rear elevation view of the push domain of theswitch of FIG. 12;

FIG. 14 is a schematic, rear elevation view of the one embodiment ofvertical push plenums of the present switch;

FIG. 15 is a schematic, front elevation view of another embodiment ofthe present network switch illustrating another method and apparatus forcooling the switch;

FIG. 16 is a schematic, cross-sectional, top plan view of the switch ofFIG. 15, taken through the line 16-16 in FIG. 15;

FIG. 17 is a schematic, cross-sectional, top plan view of anotherembodiment of the present network switch illustrating another method andapparatus for cooling the switch; and

FIG. 18 is a schematic, partially exploded, cross-sectional, top planview of the switch of FIG. 17.

DETAILED DESCRIPTION

The following detailed description describes the present embodimentswith reference to the drawings. In the drawings, reference numbers labelelements of the present embodiments. These reference numbers arereproduced below in connection with the discussion of the correspondingdrawing features.

FIG. 2 illustrates one embodiment of the present network switch 30, anda method and apparatus for cooling the switch 30. The switch 30 includesa plurality of spaced modules 32. Each module 32 is a printed circuitboard (PCB), and includes one or more integrated circuit (IC) devices34, or chips, on at least one surface. The ICs 34 generate heat, whichmust be dissipated in order to prevent a decrease in the switch'sperformance. In the illustrated embodiment, each IC 34 includes a heatsink 36, which draws heat away from the IC 34. In certain embodimentsthe ICs 34 may not include heat sinks 36, or some ICs 34 may includeheat sinks 36 and some may not.

With further reference to FIG. 2, each module 32 includes an enclosure38. The enclosures 38 help to separate airflow between the modules 32.The separation in airflow contributes to the cooling effectiveness ofthe present embodiments, as discussed in more detail below. Those ofordinary skill in the art will appreciate that in some embodiments ofthe present switch 30 some or all of the modules 32 may not includeenclosures 38. In fact, in many cases the modules 32 themselves may helpto separate airflow between modules 32.

With further reference to FIG. 2, each module 32 further includes atleast one port 40 at a first edge thereof. In certain other embodiments,however, some of the modules may not include external ports. Althoughnot visible in FIG. 2, each module 32 may include ports 40 extendingacross the switch 30 (into the plane of the paper in FIG. 2). The ports40 extend along the front face 42 and back face 44 of the switch 30 andare configured to receive cabling (not shown) to enable the switch 30 tocommunicate with other network devices. A second edge of each module 32,opposite the first edge, further includes at least one midplane 48connector 46 for connecting the PCB 32 to a midplane 48. A plurality ofpower supplies 50 provides power for the switch 30. Although only twopower supplies 50 are shown in FIG. 2, those of ordinary skill in theart will appreciate that the switch 30 may include any number of powersupplies 50. A housing or chassis 52 supports and contains the modules32.

The switch 30 includes a plurality of plenums 54, 56, 58, 60, 62, 64configured to carry cooling air. The embodiment of FIG. 2 includes sixseparate plenums 54, 56, 58, 60, 62, 64. Alternative embodiments,including those illustrated in FIGS. 6-10, may include fewer or moreplenums. The plenums 54, 56, 58, 60 in FIG. 2 are configured to delivercooling air to or from the modules 32, and the plenums 62, 64 areconfigured to deliver cooling air to or from the power supplies 50. Forsimplicity, in the present disclosure the plenums 54, 56, 58, 60 arereferred to as module cooling plenums, and the plenums 62, 64 arereferred to as auxiliary cooling plenums. In alternative embodiments,the auxiliary cooling plenums 62, 64 may be configured to delivercooling air to something other than power supplies 50, such ashigh-powered modules requiring a separate air stream.

Each of the plenums 54, 56, 58, 60, 62, 64 cooperates with a fan module66 that forces cooling air through the plenum. With reference to FIG. 3,which is a cross-sectional, top plan view of one embodiment of theswitch 30 of FIG. 2, each fan module 66 may include a plurality of fans68 extending across the switch 30. In alternative embodiments, some fanmodules may include a single fan 68. In the present disclosure, the termfan module is used broadly to cover any number of fans associated with asingle plenum.

With reference to FIG. 2, in the illustrated embodiment the modulecooling plenums 54, 56, 58, 60 are substantially L-shaped. Each includesa first portion 70 extending across the switch 30 in a front-to-backdirection, and a second portion 72 extending through the switch 30 in adirection perpendicular to the PCBs 32. A first subset of the moduleplenums 54, 56, 58, 60 is configured to deliver cooling air to the PCBs32 at the front of the switch 30, and a second subset of the module 32plenums is configured to deliver cooling air to the PCBs 32 at the backof the switch 30.

The pull plenums 56, 60 are so named because the fan modules 66associated with those plenums are located at the outlet ends of theplenums 56, 60 and are configured to pull air into and through theplenums, as indicated in FIG. 2 by the arrows having hollow arrowheads.In contrast, the push plenums 54, 58 are so named because the fanmodules 66 associated with those plenums are located at the inlet endsof the plenums 54, 58 and are configured to push air through theplenums, as indicated in FIG. 2 by the arrows having solid arrowheads.

In the illustrated configuration, the upper pull plenum 56 extendsupward through the PCBs 32 in the upper-front quadrant of the switch 30,and then horizontally along the top of the switch 30 from the front sideof the midplane 48 toward the back of the switch 30. The verticalportion 72 of the plenum 56 includes a plurality of openings 74 alongits length that enable the cooling air to flow into the plenum 56 fromthe modules 32 in the upper-front quadrant of the switch 30. The fanmodule 66 in the upper pull plenum 56 generates a pressure drop betweenthe modules 32 in the upper-front quadrant and the horizontal portion 70of the upper pull plenum 56. The fan module 66 thus sucks cooling airinto the upper-front quadrant through openings (not shown) in the frontof the switch 30. The air flows over the modules 32 and then into thevertical portion 72 of the upper pull plenum 56 through the openings 74in the vertical portion 72. The air flows through the upper pull plenum56 before being discharged at the back of the switch 30. The upper pullplenum 56 together with the modules 32 in the upper-front quadrant ofthe switch 30 defines an upper pull domain.

In the illustrated configuration, the lower pull plenum 60 extendsdownward through the PCBs 32 in the lower-front quadrant of the switch30, and then horizontally along the bottom of the switch 30 from thefront side of the midplane 48 toward the back of the switch 30. Thevertical portion 72 of the plenum 60 includes a plurality of openings 74along its length that enable the cooling air to flow into the plenum 60from the modules 32 in the lower-front quadrant of the switch 30. Thefan module 66 in the lower pull plenum 60 generates a pressure dropbetween the modules 32 in the lower-front quadrant and the horizontalportion 70 of the lower pull plenum 60. The fan module 66 thus suckscooling air into the lower-front quadrant through openings in the frontof the switch 30. The air flows over the modules 32 and then into thevertical portion 72 of the lower pull plenum 60 through the openings 74in the vertical portion 72. The air flows through the lower pull plenum60 before being discharged at the back of the switch 30. The lower pullplenum 60 together with the modules 32 in the lower-front quadrant ofthe switch 30 defines a lower pull domain.

In the illustrated configuration, the upper push plenum 54 extendshorizontally along the top of the switch 30 from the front of the switch30 toward the back side of the midplane 48. The upper push plenum 54then extends downward through the PCBs 32 in the upper-rear quadrant ofthe switch 30. The vertical portion 72 of the plenum 54 includes aplurality of openings 74 along its length that enable the cooling air toflow out of the plenum 54 and over the modules 32 in the upper-rearquadrant of the switch 30. The fan module 66 in the upper push plenum 54generates a pressure drop between air at an inlet 76 of the upper pushplenum 54 and air within the upper push plenum 54. The fan module 66thus sucks cooling air into the upper push plenum 54, forces the airthrough the plenum 54, and then forces the air through openings 74 inthe vertical portion 72 of the plenum 54 and over the modules 32 in theupper-rear quadrant. The air flows over the modules 32 in the upper-rearquadrant before being discharged at the back of the switch 30. The upperpush plenum 54 together with the modules 32 in the upper-rear quadrantof the switch 30 defines an upper push domain.

In the illustrated configuration, the lower push plenum 58 extendshorizontally along the bottom of the switch 30 from the front of theswitch 30 toward the back side of the midplane 48. The lower push plenum58 then extends upward through the PCBs 32 in the lower-rear quadrant ofthe switch 30. The vertical portion 72 of the plenum 58 includes aplurality of openings 74 along its length that enable the cooling air toflow out of the plenum 58 and over the modules 32 in the lower-rearquadrant of the switch 30. The fan module 66 in the lower push plenum 58generates a pressure drop between air at an inlet 76 of the lower pushplenum 58 and air within the lower push plenum 58. The fan module 66thus sucks cooling air into the lower push plenum 58, forces the airthrough the plenum 58, and then forces the air through openings 74 inthe vertical portion 72 of the plenum 58 and over the modules 32 in thelower-rear quadrant. The air flows over the modules 32 in the lower-rearquadrant before being discharged at the back of the switch 30. The lowerpush plenum 58 together with the modules 32 in the lower-rear quadrantof the switch 30 defines a lower push domain.

With continued reference to FIG. 2, in the pull domains each verticalportion 72 of each plenum 56, 60 includes a separate opening 74corresponding to each module 32. Suction generated by the fan modules 66thus draws air separately over each module 32. Similarly, in the pushdomains each vertical portion 72 of each plenum 54, 58 includes aseparate opening 74 corresponding to each module 32. Air pushed by thefan modules 66 thus passes separately over each module 32.Advantageously, in the illustrated cooling air distribution no module 32is located upstream or downstream of another module 32. Instead, coolingair passes over each module 32 separately so that it is not pre-heatedby passing first over one module 32 and then over another module 32.Further, the enclosures 38 separate the airflow between modules 32, sothat there is no mixing of cooling air streams. The present switch 30and methods for cooling the switch 30 thus eliminate the problem ofstack rise that plagues other switches and network devices. Further,each of the cooling domains are isolated from one another, so thatheated air from one domain is not carried into another domain. Those ofordinary skill in the art will appreciate that in certain embodimentsthe modules 32 themselves may perform the function of separating theairflow between modules 32.

In the illustrated embodiment, the openings 74 are represented as beingrelatively large and rectangular. Those of ordinary skill in the artwill appreciate that the openings 74 could have other configurations.For example, the openings could have a different size and/or shape. Theopenings could also be small perforations, rather than large openings.

FIG. 3 is a cross-sectional, top plan view of one embodiment of theswitch 30 of FIG. 2, taken through the line 3-3 in FIG. 2. FIG. 4 is across-sectional, top plan view of one embodiment of the switch 30 ofFIG. 2, taken through the line 4-4 in FIG. 2. FIGS. 3 and 4 illustratethe pattern of air distribution in the switch 30 from the upperperspective. In FIG. 3, the solid arrows indicate air that is flowing inthe upper plenums 54, 56, and the dashed arrows indicate air that isflowing across the modules 32, since the modules 32 are not visible inFIG. 3. FIGS. 3 and 4 further illustrate one possible configuration foreach plenum, in which each plenum includes three vertical airdistribution channels 72. Other embodiments may include a differentnumber of vertical air distribution channels for each module plenum 54,56, 58, 60 such as two vertical air distribution channels per plenum.Accordingly, FIGS. 3 and 4 should not be interpreted as limiting.

In FIG. 3, the arrows having solid arrowheads illustrate the pattern ofair distribution in the push domains. Cooling air enters the switch 30from the front and flows through the fan module 66 and into thehorizontal portion 70 of the push plenum 54, 58. With reference to FIG.2, the push plenums 54, 58 are located above and below the modules 32.With reference to FIG. 3, within the horizontal portion 70 of the pushplenum 54, 58 the air converges into first and second fingers 78 beforeentering first, second and third vertical air distribution channels 72.The air distribution channels 72 are arranged across the switch 30 withchannels at either side and channels extending through the side-to-sidecenter of the switch 30. As shown in FIG. 4, after flowing verticallythrough the air distribution channels 72 the cooling air exits thechannels 72 through the openings 74 (FIG. 2) and flows over the modules32 at the rear of the switch 30 before exiting the switch 30 at therear.

FIG. 5 is a rear elevation view of the push domains of the switch 30 ofFIG. 2. The pull domains have been removed for clarity.

The arrows in FIG. 5 illustrate the pattern of air distribution in thepush domains from the rear perspective. Cooling air exits the fanmodules 66 and is forced into the air distribution channels 72 throughthe openings 74 (FIG. 2). After flowing vertically through the airdistribution channels 72 the cooling air exits the air distributionchannels 72 through the openings 74 (FIG. 2) and flows over the modules32 at the rear of the switch 30 before exiting the switch 30 at therear.

With reference to FIG. 3, the arrows having hollow arrowheads illustratethe pattern of air distribution in the pull domains. Cooling air entersthe switch 30 from the front and flows over the modules 32 (not visiblein FIG. 3) at the front of the switch 30. The cooling air then convergesbetween the vertical air distribution channels 72 and enters thechannels 72. After flowing vertically through the air distributionchannels 72 the cooling air exits the channels 72 through the openings74 (FIG. 2) and flows into the pull plenum 56, 60. The cooling air thenflows through the pull plenum 56, 60 and through the fan module 66before exiting the switch 30 at the rear.

With reference to FIG. 2, the switch 30 further includes upper and lowerauxiliary cooling plenums 62, 64. Each of the auxiliary plenums 62, 64is substantially horizontal, and extends through the switch 30 fromfront to back. A fan module 66 in each auxiliary plenum 62, 64 sucks incooling air from the front of the switch 30, forces the air through theplenum and discharges it at the back of the switch 30. As the coolingair flows through the plenum it flows over the power supply 50 and keepsthe power supply 50 cool. In the illustrated embodiment, the fan modules66 in the upper and lower auxiliary plenums 62, 64 are located adjacentthe front of the switch 30, which is also the inlet side of the switch30. Those of ordinary skill in the art will appreciate that the fanmodules 66 could be located adjacent the back of the switch 30, and/orthe direction of airflow through the switch 30 generated by the fanmodules 66 could be reversed (back to front). Those of ordinary skill inthe art will also appreciate that fan modules 66 could be locatedadjacent both the front and the back of the switch 30.

FIGS. 6 and 7 illustrate an alternate configuration for the presentswitch 73. FIG. 6 is a schematic, cross-sectional, top plan view, andFIG. 7 is a schematic, rear elevation view. Further, FIGS. 6 and 7illustrate only the push domains. The pull domains have been removed forclarity. With reference to FIG. 6, the push plenums 75 include fivefingers 77, in contrast to the two fingers 78 in the switch 30 of FIG.3. Cooling air entering the push plenums 75 converges into the fivefingers 77 and then enters the vertical air distribution channels 79.The switch 73 of FIG. 6 includes six air distribution channels 79arranged in spaced relation to one another across the switch 73. Withreference to FIGS. 6 and 7, after travelling through the airdistribution channels 79 the cooling air flows out of openings (notshown) in the channels 79 and then flows across the PCBs 81. In theswitch 73 of FIGS. 6 and 7 the PCBs 81 are arranged so that a planedefined by each is parallel to the air distribution channels 79, ratherthan the perpendicular arrangement of the switch 30 of FIG. 2. Withreference to FIG. 7, each module 81 has a dedicated air distributionchannel 79, so that each module 81 receives a separate supply of coolingair. Like the switch 30 of FIG. 22, then, the switch 73 of FIGS. 6 and 7eliminates stack rise. After passing across the modules 81, the coolingair exits the back of the switch 73.

FIGS. 8-10 illustrate further embodiments of the present network switch80, 82, 84 and methods and apparatus for cooling the switches. Theembodiments of FIGS. 8-10 apply many of the same cooling principlespresent in the switch 30 of FIG. 2, and achieve many of the sameadvantages. With reference to FIG. 8, the switch 80 includes fourseparate module cooling domains, as in the switch 30 of FIG. 2. Theswitch 80 of FIG. 8 does not, however, include separate auxiliarycooling plenums/domains. As with the switch 30 of FIG. 2, the switch 80of FIG. 8 includes upper and lower push plenums 86, 88 and upper andlower pull plenums 90, 92. In FIG. 8, however, each module 94 isoriented vertically instead of horizontally as in FIG. 1. Cooling airenters from the front of the switch 80, passes separately over themodules 94 and through the plenums 86, 88, 90, 92, and exits at the rearof the switch 80. The cooling air flows horizontally over the modules94. Again, each module 94 receives a separate supply of cooling air,thus eliminating stack rise.

The switch 82 of FIG. 9 is similar to the switch 80 of FIG. 8, exceptthat it includes only two cooling plenums/domains. The illustratedembodiment includes an upper push plenum 96 and an upper pull plenum 98.Alternative embodiments may include a lower push plenum and a lower pullplenum, or one upper plenum and one lower plenum. The switch 84 of FIG.10 is similar to the switch 82 of FIG. 9, except that the cooling airflows vertically over the modules 100. In the pull domain, the coolingair enters at the bottom of the switch 84 and flows upward over themodules 100. In the push domain, the cooling air flows downward over themodules 100 and exits at the bottom of the switch 84.

FIGS. 11 and 11A illustrate an alternative embodiment of pull domainsfor the present switches. In contrast to the pull domains in the switch30 of FIG. 2, the openings 104 in the air distribution channels 106 inFIGS. 11 and 11A vary in size. FIG. 11A provides a detail view of theopenings 104. In the upper pull domain 108, the openings 104 decrease insize from bottom to top, and in the lower pull domain 110, the openings104 decrease in size from top to bottom. This arrangement corresponds tothe decreasing pressure drop with increasing distance from the fanmodule 66. The openings 104 closest to the vertical center of the switchare farthest away from their respective fan modules 66. The pressuredrop between these openings 104 and their respective fan modules 66 isthus less than the pressure drop between the openings 104 adjacent thetop and bottom of the switch and their respective fan modules 66. Thevariable size openings 104 compensate for these differences in pressuredrop. Openings 104 having a relatively large pressure drop havecorrespondingly small areas, and openings 104 having a relatively smallpressure drop have correspondingly large areas. The suctions at eachopening are thus substantially equal. The substantially equal suctionscontribute to the fan module's ability to draw an approximately equalamount of cooling air over each PCB 32, which provides equal cooling toeach PCB 32. In an alternative embodiment, the discrete openings shownin FIGS. 11 and 11A may be replaced with perforations, with a sizeand/or density of the perforations varying along the length of the airdistribution channels.

FIGS. 12-14 illustrate an alternative embodiment of push domains 118,120 for the present switches. With reference to FIG. 12, the openings114 in the air distribution channels 116 are all substantially equal insize. FIG. 13 illustrates the push domains 118, 120 from a rearperspective, and FIG. 14 illustrates four of the air distributionchannels 116 of the push domains 118, 120 from the same perspective.FIG. 14 also illustrates one module enclosure 38 for clarity. Withreference to FIG. 14, the openings 114 in the air distribution channels116 include baffles 122. The baffles 122 compensate for the decreasingair velocity with increasing distance from the fan modules 66. In theupper push domain 112 the air in the upper portions of the upper airdistribution channels 116 has greater velocity than the air in the lowerportions of the upper air distribution channels 116. Similarly, in thelower push domain 112 the air in the lower portions of the lower airdistribution channels 116 has greater velocity than the air in the upperportions of the lower air distribution channels 116.

The baffles 122 are oriented at an angle with respect to the directionof travel of air through the air distribution channels 116. In theillustrated embodiment, the baffle angle is approximately 45°. However,in other embodiments the baffle angle may be more or less than 45°. Theangled baffles 122 redirect a portion of the air flowing past eachopening 114, such that some air is directed through the opening 114 andsome passes the opening 114 and continues through the air distributionchannel 116. Without the baffles 122, less air would flow through theupstream openings 114 as compared to the downstream openings 114. Thebaffles 122 even out the distribution of cooling air flowing through theopenings 114 so that each module 32 receives a roughly equal amount ofcooling air.

FIGS. 15 and 16 illustrate an alternative switch 124. FIG. 15 is a frontview of the push domains 126, 128, and FIG. 16 is a top cross-sectionalview of the switch 124 taken through the line 15-15 in FIG. 15. Theswitch 124 is similar to the switch 30 of FIG. 2, except that itincludes external air ducts 130 that increase the switch's cooling aircapacity. With reference to FIG. 15, the external ducts 130 runvertically along the sides of the switch 124. With reference to FIG. 16,the external ducts 130 run adjacent to the air distribution channels132, but on the outside of the switch chassis 134. The external ducts130 are in fluid communication with their adjacent air distributionchannels 132 through perforations 136 in the switch chassis 134. Airthus flows vertically through both the air distribution channels 132 andthe external ducts 130. The external ducts 130 increase the volumeavailable for carrying air vertically through the switch 124, thusincreasing the switch's cooling capacity.

With reference to FIGS. 15 and 16, the external ducts 130 reside withina dead space 138 in a mounting rack 140 that supports the switch 124.The rack 140 includes a base 142. A pair of front mounting rails 144 anda pair of rear mounting rails 146 extend vertically from the base 142.As shown in the front view of FIG. 15, the rails 144, 146 provide asmall clearance to enable the switch 124 to be slid into the rack 140from either the front or back side. However, the width of the switch 124including the external ducts 130 is greater than the side-to-sidedistance between the rails 144, 146. Thus, in one embodiment theexternal ducts 130 are secured to the switch chassis 134, but aredeformable or collapsible to enable the switch 124 to fit into the rack140. As the switch 124 slides into the rack 140 and the external ducts130 squeeze past the rails 144, 146, the ducts 130 collapse against theswitch 124. After the ducts 130 clear the rails 144, 146 they expandoutward again into the configuration shown in FIGS. 15 and 16. The ducts130 may be constructed of a flexible and resilient material to enablethem to deform and rebound to their original shape. In other embodimentsthe ducts 130 may be constructed of a flexible but non-resilientmaterial that is supported by resilient members (not shown). The archedshape of the ducts 130 (FIG. 16) facilitates their ability to collapseand rebound to their original shape.

In still other embodiments the ducts may be constructed of a rigidmaterial. For example, FIGS. 17 and 18 illustrate one example of ducts148 that are installed within the rack 140 prior to inserting the switch150. FIG. 17 illustrates the switch 150 in its final position within therack 140, and FIG. 18 illustrates the switch 150 just before it is slidinto the rack 140. Because the ducts 148 are installed in the rack 140prior to inserting the switch 150, they need not deform during theswitch installation process. Instead, the ducts 148 seal around theperforations 136 in the switch chassis 134 as the switch 150 slides intoits final position (FIG. 17). As shown in FIGS. 17 and 18, theillustrated switch 150 includes gaskets 152 extending along the outsideof the switch chassis 134 around the perforations 136. The gaskets 152compress and seal against edges of the ducts 148 to prevent leaking ofcooling air. In alternative embodiments the gaskets 152 may be securedto the ducts 148, rather than the switch chassis 134. In the illustratedembodiment the ducts 148 have a rectangular cross-section. However,those of ordinary skill in the art will appreciate that the ducts 148could have alternative shapes.

With reference to FIG. 17, in one embodiment the gaskets 152 may havedifferent heights, and the ducts 148 may extend toward the switch 150 bydifferent amounts. For example, in FIG. 17 a first pair of the gaskets152, labeled “1,” has a first height, a second pair of the gaskets 152,labeled “2,” has a second greater height, a third pair of the gaskets152, labeled “3,” has a third even greater height. Similarly, theportions of the ducts 148 that engage the first pair of the gaskets 152extends farther toward the switch 150 than the portions of the ducts 148that engage the second and third pairs of the gaskets 152, and theportions of the ducts 148 that engage the second pair of the gaskets 152extends farther toward the switch 150 than the portions of the ducts 148that engage the third pair of the gaskets 152. With this configuration,as the switch 150 is slid into the rack 140 the gaskets 152 don'tinterfere with the ducts 148 until the switch 150 is in its finalposition within the rack 140.

In the figure descriptions contained herein, terms such as horizontal,vertical, top, bottom, upper, lower, front, back, etc. are used withreference to the illustrated orientation of the apparatus beingdescribed. In alternative embodiments, the apparatus may be orienteddifferently. Accordingly, terms such as horizontal, vertical, top,bottom, upper, lower, front, back, etc. should not be interpreted aslimiting.

SCOPE OF THE DISCLOSURE

The above description presents the best mode contemplated for carryingout the present apparatus and methods for cooling network switches, andthe manner and process of making and using it, in such full, clear,concise, and exact terms as to enable any person skilled in the art towhich it pertains to make and use this apparatus and practice thesemethods. This apparatus and these methods are, however, susceptible tomodifications and alternate constructions from that discussed above thatare fully equivalent. Consequently, this apparatus and these methods arenot limited to the particular embodiments disclosed. On the contrary,this apparatus and these methods cover all modifications and alternateconstructions coming within the spirit and scope of the apparatus andmethods as generally expressed by the following claims, whichparticularly point out and distinctly claim the subject matter of theapparatus and methods.

1. A network switch, comprising: a plurality of spaced printed circuitboards (PCBs); a plurality of fan modules configured to force coolingair through the switch; a plurality of plenums configured to carry theforced cooling air, each plenum being associated with at least one ofthe fan modules; wherein the plenums are configured to distribute thecooling air throughout the switch so that no PCB is located upstreamfrom any other PCB, and therefore no PCB preheats the cooling airreceived by any other PCB; and further wherein each plenum includes anelongate portion extending through the switch substantiallyperpendicularly to the PCBs, the elongate portion including an openingassociated with each PCB.
 2. The switch of claim 1, wherein the openingsvary in size.
 3. The switch of claim 2, wherein the openings becomeincreasingly larger with increasing distance from the fan modules.
 4. Anetwork switch comprising: a plurality of spaced printed circuit boards(PCBs); a plurality of fan modules configured to force cooling airthrough the switch; a plurality of plenums configured to carry theforced cooling air, each plenum being associated with at least one ofthe fan modules; wherein the plenums are configured to distribute thecooling air throughout the switch so that no PCB is located upstreamfrom any other PCB, and therefore no PCB preheats the cooling airreceived by any other PCB; and further wherein each of the plenums isL-shaped in profile and includes a first portion that extends across theswitch in a direction parallel to the PCBs, and a second portion thatextends through the switch in a direction perpendicular to the PCBs. 5.The switch of claim 4, wherein the switch includes a midplane.
 6. Theswitch of claim 5, wherein for a first subset of the plenums the firstportion extends perpendicularly to the midplane to a first side of themidplane and across the midplane, and the second portion extendsparallel to the midplane to a second side of the midplane, and for asecond subset of the plenums the first portion extends perpendicularlyto the midplane to the second side of the midplane and across themidplane, and the second portion extends parallel to the midplane to thefirst side of the midplane.
 7. A network switch, comprising: a pluralityof spaced printed circuit boards (PCBs); a plurality of fan modulesconfigured to force cooling air through the switch; a plurality ofplenums configured to carry the forced cooling air, each plenum beingassociated with at least one of the fan modules; wherein the plenums areconfigured to distribute the cooling air throughout the switch so thatno PCB is located upstream from any other PCB, and therefore no PCBpreheats the cooling air received by any other PCB; and further whereinthe switch is divided into four independent cooling domains, includingan upper push domain, a lower push domain, an upper pull domain, and alower pull domain.
 8. The switch of claim 7, wherein in the push domainscooling air passes first through one of the plenums and then across oneof the PCBs, and in the pull domains cooling air passes first across oneof the PCBs and then through one of the plenums.
 9. A method of coolinga network switch, the switch including a plurality of spaced printedcircuit boards (PCBs), each PCB including at least one integratedcircuit (IC) device thereon, the method comprising the steps of: forcingcooling air through the switch such that each of the plurality of spacedPCBs receives cooling air; and distributing the cooling air throughoutthe switch such that no PCB is located upstream from any other PCB, andtherefore no PCB preheats the cooling air received by any other PCB; andfurther wherein the cooling air travels through a plurality of plenums,each plenum including an elongate portion extending through the switchsubstantially perpendicularly to the PCBs, the elongate portionincluding an opening associated with each PCB.
 10. The method of claim9, wherein the cooling air travels through a first portion of eachplenum that extends across the switch in a direction parallel to thePCBs, and through a second portion that extends through the switch in adirection perpendicular to the PCBs.
 11. A method of cooling a networkswitch, the switch including a plurality of spaced printed circuitboards (PCBs), each PCB including at least one integrated circuit (IC)device thereon, the method comprising the steps of: forcing cooling airthrough the switch such that each of the plurality of spaced PCBsreceives cooling air; and distributing the cooling air throughout theswitch such that no PCB is located upstream from any other PCB, andtherefore no PCB preheats the cooling air received by any other PCB; andfurther wherein the cooling air is divided into four independent coolingdomains, including an upper push domain, a lower push domain, an upperpull domain, and a lower pull domain.
 12. A network switch, comprising:a plurality of spaced printed circuit boards (PCBs); a plurality of fanmodules configured to force cooling air through the switch; a pluralityof plenums configured to carry the forced cooling air, each plenum beingassociated with at least one of the fan modules; wherein the plenums areconfigured to distribute the cooling air throughout the switch so thatcooling air entering the switch passes across only one of the PCBsbefore exiting the switch; and further wherein each plenum includes aportion extending perpendicularly to the PCBs and having a plurality ofopenings along its length, and each opening is located adjacent one ofthe PCBs so that cooling air entering any opening will have passedacross only one of the PCBs before exiting the switch and cooling airexiting any opening passes across only one of the PCBs before exitingthe switch.
 13. The switch of claim 12, wherein the switch includes amidplane.
 14. A network switch, comprising: a plurality of spacedprinted circuit boards (PCBs); a plurality of fan modules configured toforce cooling air through the switch; a plurality of plenums configuredto carry the forced cooling air, each plenum being associated with atleast one of the fan modules; wherein the plenums are configured todistribute the cooling air throughout the switch so that cooling airentering the switch passes across only one of the PCBs before exitingthe switch; and further wherein each of the plenums is L-shaped inprofile and includes a first portion that extends across the switch in adirection parallel to the PCBs, and a second portion that extendsthrough the switch in a direction perpendicular to the PCBs.
 15. Theswitch of claim 14, wherein for a first subset of the plenums the firstportion extends perpendicularly to the midplane to a first side of themidplane and across the midplane, and the second portion extendsparallel to the midplane to a second side of the midplane, and for asecond subset of the plenums the first portion extends perpendicularlyto the midplane to the second side of the midplane and across themidplane, and the second portion extends parallel to the midplane to thefirst side of the midplane.
 16. A network switch, comprising: aplurality of spaced printed circuit boards (PCBs); a plurality of fanmodules configured to force cooling air through the switch; a pluralityof plenums configured to carry the forced cooling air, each plenum beingassociated with at least one of the fan modules; wherein the plenums areconfigured to distribute the cooling air throughout the switch so thatcooling air entering the switch passes across only one of the PCBsbefore exiting the switch; and further wherein the switch is dividedinto four independent cooling domains, including an upper push domain, alower push domain, an upper pull domain, and a lower pull domain. 17.The switch of claim 16, wherein in the push domains cooling air passesfirst through one of the plenums and then across one of the PCBs, and inthe pull domains cooling air passes first across one of the PCBs andthen through one of the plenums.
 18. A method of cooling a networkswitch, the switch including a plurality of spaced printed circuitboards (PCBs), each PCB including at least one integrated circuit (IC)device thereon, the method comprising the steps of: forcing cooling airthrough the switch such that each of the plurality of spaced PCBsreceives cooling air; and distributing the cooling air throughout theswitch such that no PCB is located upstream from any other PCB, andtherefore no PCB preheats the cooling air received by any other PCB;wherein the cooling air travels through a plurality of plenums, eachplenum including an elongate portion extending through the switchsubstantially perpendicularly to the PCBs, the elongate portionincluding an opening associated with each PCB; further wherein thecooling air is divided into four independent cooling domains, includingan upper push domain, a lower push domain, an upper pull domain, and alower pull domain; and further wherein in the push domains the coolingair passes first through one of the plenums and then across one of thePCBs, and in the pull domains the cooling air passes first across one ofthe PCBs and then through one of the plenums.